A B S T R A C T The initial step in the degradation pathways of proline and hydroxyproline is catalyzed by proline oxidase and hydroxyproline oxidase, yielding A1-pyrroline-5-carboxylate and A1-pyrroline-3-hydroxy-5-carboxylate, respectively. The second step is the oxidation of A1-pyrroline-5-carboxylate to glutamate and Al-pyrroline-3-hydroxy-5-carboxylate to y-hydroxyglutamate. To determine if this second step in the degradation of proline and hydroxyproline is catalyzed by a common or by separate enzyme(s), we developed a radioisotopic assay for Al-pyrroline-3-hydroxy-5-carboxylate dehydrogenase activity. We then compared Al-pyrroline-3-hydroxy-5-carboxylate dehydrogenase activity with that of Al-pyrroline-5-carboxylate dehydrogenase in fibroblasts and leukocytes from type II hyperprolinemia patients, heterozygotes, and controls. We found that cells from type II hyperprolinemia patients were deficient in both dehydrogenase activities. Furthermore, these activities were highly correlated over the range found in the normals, heterozygotes, and patients.We conclude from these data that a common Alpyrroline-5-carboxylate dehydrogenase catalyzes the oxidation of both Al-pyrroline-5-carboxylate and Alpyrroline-3-hydroxy-5-carboxylate, and that this activity is deficient in type II hyperprolinemia.

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